Ribbon spool, ribbon cassette, and printing apparatus

ABSTRACT

A ribbon spool is detachably attached to a printing apparatus for forming an image on a recording medium by using an ink ribbon. The printing apparatus has an engaging member including an engaging convex portion for engaging the ribbon spool. The ribbon spool includes a ribbon retaining portion for retaining the ink ribbon, and an engaging portion provided at one lateral side end of the ribbon spool for engaging the engaging convex portion and having a plurality of inclined grooves. The grooves have a different inclination angle from that of a lateral side face of the engaging convex portion. At least one of the grooves of the engaging portion has a point contact with the engaging convex portion at two points to engage the engaging convex portion.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to a ribbon spool, a ribbon cassette, anda printing apparatus. In particular, the present invention relates to aprinting apparatus that forms an image on a recording medium by using aribbon spool detachably attached to the printing apparatus, a ribboncassette including the ribbon spool, and an ink ribbon.

Conventionally, a printing apparatus has been known to be used toprepare a card such as a credit card, a cash card, a license card, or anID card, for example. In the case of the printing apparatus as describedabove and an image recording apparatus through which a plain paper or athermosensitive paper can be printed, an image is generally printed viaan ink ribbon stored in a cartridge onto a card or a recording paperthat is pushed to a thermal head and that has one surface supported by aplaten roller for example. The ink ribbon is generally retained by aribbon spool. The ribbon spool is connected to the body of the printingapparatus to carry the ink ribbon, thereby conducting a printingoperation.

The ribbon spool may be connected to the printing apparatus in variousforms. One of such forms of connections, for example, is to form a notchat one end of the ribbon spool to engage the notch with a protrusionprovided in a printing apparatus. Another form of such connections isdisclosed in Japanese Patent Examined Publication No. H07-100555 (PatentDocument 1). In Patent Document 1, an engaging portion is provided atthe inner side of a cylindrical ribbon spool and is inserted to aprinting apparatus having a spool axis.

When an ink ribbon is continually subjected to a printing operation, theink ribbon has different roll diameters at the supply side and at therolled side. A small roll diameter and a large roll diameter causedifferences in amounts of ink ribbons to be carried. To prevent thisproblem, a printing apparatus has been developed and disclosed inJapanese Patent Laid-Open No. 05-330209 (Patent Document 2). In PatentDocument 2, an encoder for detecting the carrying amount of the inkribbon is provided, and a rotation amount detection mechanism of theribbon spool (encoder) is installed in a driving transmission system ofthe ribbon spool.

In the case of the above printing apparatus, however, the concaveportion of any one of the ribbon spool and the engaging portion of theprinting apparatus is engaged with the convex portion having the sameshape (or the concave portion has a contact with the convex portion in alinear manner), and, thus, it results in a gap in the engaging portion.In the case of the engaging portion as described above, a backlash isgenerated in the engaging portion (driving transmission system) during aprinting operation (or at the moment when the head is raised at thecompletion of the printing). Since the printing apparatus has astructure in which the encoder is installed in the ribbon spool drivingtransmission system, the backlash generated in the driving transmissionsystem has a disadvantageous influence that generates a differencebetween the actual rotation amount of the ribbon spool and the rotationamount detected by the encoder. The difference between the actualrotation amount of the ribbon spool and the rotation amount detected bythe encoder impairs an accuracy of a ribbon locating. Particularly, whenthe difference between the actual rotation amount of the ribbon spooland the rotation amount detected by the encoder occurs at the same timethe ribbon passes by a sensor, this difference remains and impairs thesubsequent ribbon locating, and therefore, it may result in differentcolors to be printed in the worst case.

In view of the problems stated above, it is an objective of the presentinvention to provide a ribbon spool engaging with an engaging member ofa printing apparatus without a backlash, a ribbon cassette having theribbon spool, and a printing apparatus engaging the ribbon spool withoutthe backlash.

Further objects and advantages of the invention will be apparent fromthe following description of the invention.

SUMMARY OF THE INVENTION

In order to achieve the above objective, as for the first aspect of thepresent invention, a ribbon spool is detachably attached to a printingapparatus, said printing apparatus including an engaging member havingan engaging convex portion engaged with an engaging portion of a ribbonspool and using an ink ribbon to form an image on a recording medium.The ribbon spool comprises: a ribbon retaining portion for retaining theink ribbon; and an engaging portion provided at one side end and havinga plurality of inclined grooves. The grooves of the engaging portionhave a different inclination angle from that of a side face of theengaging convex portion engaging with the engaging portion. At least onegroove of the grooves of the engaging portion is in a point contact withthe engaging convex portion at two points to be engaged therewith.

According to the first aspect, the ribbon spool includes the ribbonretaining portion for retaining an ink ribbon and the engaging portionthat is provided at one side end and that has a plurality of inclinedgrooves. The engaging portion has grooves having a different inclinationangle from that of the side face of the engaging convex portion engagedwith the engaging portion. At least one of the grooves of the engagingportion is in a point contact with the side face of the engaging convexportion at two points. According to this aspect of the invention, atleast one of the grooves of the engaging portion is in a point contactwith the side face of the engaging convex portion at two points to beengaged therewith. This configuration prevents a backlash when theengaging portion of the ribbon spool is engaged with the engaging convexportion of the engaging member of the printing apparatus. Thus, on theprinting apparatus side, the actual rotation amount of the ribbon spoolcan be accurately detected by an encoder.

According to the first aspect, convex portions forming the grooves ofthe engaging portion preferably have a different shape from the shape ofthe engaging convex portion. When the grooves of the engaging portionhave an inclination angle α, the side face of the engaging convexportion has an inclination angle β, and α is 0°<α<90° (where α<β), it isdesirable that the two points correspond inclined surfaces of the convexportions forming the grooves of the engaging portion and vertexes of theengaging convex portion. When α is 90°≦α<180° (where β<90°), the twopoints correspond vertexes of the convex portions forming the grooves ofthe engaging portion and side faces of the engaging convex portion. Theribbon retaining portion has a flange that regulates the position of theink ribbon in an axial direction, and the engaging portion may beprovided to be adjacent to the flange.

In order to overcome the above disadvantage, according to the secondaspect of the present invention, a ribbon cassette includes a supplyspool for supplying an ink ribbon, a winder spool around which the inkribbon is wound, and a case for storing the supply spool and the winderspool in a rotatable manner. The ribbon spool according to the firstaspect is provided to at least one of the supply spool and the winderspool. The second aspect of the invention also can provide the sameeffect as that of the first aspect.

In order to overcome the above disadvantage, according to the thirdaspect of the present invention, a printing apparatus has an engagingmember engaged with an engaging portion of a ribbon spool including aribbon retaining portion for retaining an ink ribbon and the engagingportion that is provided at one side end and that has a plurality ofinclined grooves, and the printing apparatus uses the ink ribbon to forman image on a recording medium. The engaging member has an engagingconvex portion engaged with at least one groove of the grooves of theengaging portion, a side face of the engaging convex portion engagedwith the engaging portion has a different inclination angle from thoseof the grooves of the engaging portion, and the engaging convex portionhas a point contact with the at least one groove at two points.According to the third aspect of the invention, the engaging convexportion of the printing apparatus is in a point contact with at leastone groove of the grooves of the engaging portion of the ribbon spool attwo points to be engaged therewith. This configuration prevents abacklash when the engaging convex portion of the printing apparatus isengaged with the engaging portion of the ribbon spool. Thus, the actualrotation amount of the ribbon spool can be accurately detected.

According to the third aspect, the engaging convex portion preferablyhas a different shape from those of the convex portions forming thegrooves of the engaging portion. When the grooves of the engagingportion have an inclination angle α, the side face of the engagingconvex portion has an inclination angle β, and α is 0°<α<90° (whereα<β), it is desirable that the two points correspond inclined surfacesof the convex portions forming the grooves of the engaging portion andvertexes of the engaging convex portion. When α is 90°≦α<180° (whereβ<90°), the two points correspond vertexes of the convex portionsforming the grooves of the engaging portion and side faces of theengaging convex portion. The engaging member has a biasing means forbiasing the ribbon spool and the biasing means may bias the engagingconvex portion toward the engaging portion. The engaging member may beconnected to an encoder for detecting a rotation amount of the ribbonspool.

According to the first and second aspects of the present invention, atleast one groove of the engaging portion has a point contact with theside faces of the engaging convex portion at two points to be engagedtherewith. Therefore, a backlash can be advantageously prevented whenthe engaging portion of the ribbon spool is engaged with the engagingconvex portion of the engaging member of the printing apparatus.According to the third aspect, the engaging convex portion of theprinting apparatus is in a point contact with at least one groove of theengaging portion of the ribbon spool to be engaged therewith. Thisconfiguration can advantageously prevent a backlash when the engagingconvex portion of the printing apparatus is engaged with the engagingportion of the ribbon spool, thus accurately detecting the actualrotation amount of the ribbon spool.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating a printer apparatus to whichthe present invention can be applied.

FIG. 2 is a schematic cross-portional view illustrating the printerapparatus in which a cleaning roller and a carry roller are positionedat the first position.

FIG. 3 is a perspective view illustrating a ribbon cassette detachablyattached to the printer apparatus.

FIG. 4 is a perspective view illustrating an engaging portion of theprinter apparatus engaged with a spool body of a winder spool.

FIGS. 5A to 5C schematically illustrate how the engaging portion of theprinter apparatus engages the engaging portion of a supply spool,wherein FIG. 5A illustrates how the engaging portion of the printerapparatus of the embodiment is engaged with the engaging portion of thesupply spool, FIG. 5B illustrates how the engaging portion of theprinter apparatus engages the engaging portion of the supply spoolaccording to another embodiment, and FIG. 5C illustrates how theengaging portion of the printer apparatus engages the engaging portionof the supply spool according to another embodiment.

FIG. 6 schematically illustrates how a tip end of an engaging convexportion provided in the engaging member of the printer apparatus of theembodiment abuts against a tip end of the convex portion of the engagingportion of the spool body.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, with reference to the drawings, embodiments will bedescribed, wherein the present invention is applied to a printerapparatus for printing characters or an image on a card-like recordingmedium (hereinafter simply referred to as a card).

The printer apparatus of this embodiment is connected to a high orderapparatus (e.g., a host computer such as a personal computer) via aninterface (not shown). Printing record data or magnetic recording dataor the like can be transmitted from the high order apparatus to theprinter apparatus to instruct a recording operation or the like. It isnoted that, as described later, the printer apparatus has an operationpanel portion (operation display portion) 105 (see FIG. 1) through whicha recording operation instruction from the high order apparatus can bereceived. A recording operation instruction also can be sent from theoperation panel portion 105. The high order apparatus is generallyconnected to an image input apparatus for reading an image recorded on adocument (e.g., scanner), an input apparatus for inputting aninstruction or data to the high order apparatus (e.g., keyboard, mouse),and a monitor for displaying data or the like generated by the highorder apparatus (e.g., liquid crystal display).

As shown in FIG. 1, the printer apparatus 100 of this embodimentincludes: a card supply portion 110 that is provided at one side of acasing 102, that can store therein a plurality of layered blank cards(about 100 blank cards) not yet subjected to a recording processing, andthat is detachably attached to the casing 102; a card container 120 thatis similarly provided at the one side of the casing 102 and at the lowerpart of the card supply portion 110, that can store therein cards (about30 cards) subjected to the recording processing in an inclined manner,and that is detachably attached to the casing 102; a display portion 104that is provided at the one side of the casing 102 and at a positionadjacent to the card supply portion 110 and that displays an operationstate including an error state of the printer apparatus 100; and anoperation panel portion 105 for carrying out various settings such as aprinting processing or a magnetic recording processing. It is noted thatthe operation panel portion 105 is attached so as to be synchronous withthe rotation of a dial 106.

A part of the card container 120 has a card outlet 121 through whichcards that are subjected to the recording processing and that cannot bestored anymore in the card container 120 can be discharged to theexterior of the apparatus. One face of the printer apparatus 100 has anopen/close cover 107 that is used to provide an access to the interiorof the apparatus in order to attach or detach a ribbon cassette 152including an ink ribbon R used for printing and recording operations.The open/close cover 107 constitutes apart of the casing 102.

A basic structure of the printer apparatus 100 is disclosed in U.S.patent application Ser. No. 12/003,260, the disclosure of which isincorporated herein.

The following portion will describe the ribbon cassette 152 detachablyattached to the apparatus body of the printer apparatus 100 of thisembodiment.

As shown in FIG. 3, the ribbon cassette 152 includes: a supply spool 154that supplies the ink ribbon R; a winder spool 155 around which the inkribbon R is wound; and a cassette case 30 that stores the supply spool154 and the winder spool 155 via a notch 30A (or while the supply spool154 and the winder spool 155 being axially supported by the notch 30A)in a rotatable manner. The supply spool 154 and the winder spool 155have therebetween the ink ribbon R exposed out of the cassette case 30so that the ink ribbon R can be abutted to a thermal head 151 (whichwill be described later) (see FIG. 2). It is noted that the ribboncassette 152 has a roller-like cleaner 132 that is engaged with acleaning roller 131 (which will be described later) to remove the dustattached to the cleaning roller 131.

FIG. 4 illustrates how the engaging portion 12 of the winder spool 155is engaged with an engaging member 23 of the apparatus body (engagingconvex portion 22). The supply spool 154 and the winder spool 155 shownin FIG. 3 are obtained by winding (or retaining) the ink ribbon R arounda spool body 10, respectively. The ink ribbon R not yet used is woundaround the supply spool 154. The ink ribbon R already used (the inkribbon R already subjected to the thermal transfer by the thermal head151) is wound around the winder spool 155.

The spool body 10 has: the cylindrical ribbon retaining portion 18 thathas flanges 13 and 14 at both sides and that retains the ink ribbon R;the engaging portion 12 that is provided at one side end so as to beadjacent to the flange 13; and an axis portion 19 that is provided atthe opposite side of the engaging portion 12 so as to be adjacent to theflange 14 and that has a smaller diameter than that of the cylindricalportion of the ribbon retaining portion 18.

The flanges 13 and 14 regulate the position of the ink ribbon R woundaround the ribbon retaining portion 18 in the axial direction of thespool body 10. Thus, even when the spool body 10 is rotated, thenot-yet-used ink ribbon R is supplied without being dislocated from theribbon retaining portion 18 (in the case of the supply spool 154) andthe already-used ink ribbon R is appropriately wound around a ribbonretaining portion 18 (in the case of the winder spool 155). It is notedthat the axis portion 19 is rotatably supported by a circular notch (notshown) formed in the cassette case 30.

The engaging portion 12 has six trapezoidal convex portions protrudingin the end direction (the left side of FIG. 4). In other words, as shownin FIG. 3, the engaging portion 12 has grooves each of which is formedby an inclined surface 12A that is formed at the side face of the convexportion to draw a straight line and that has a predetermined inclinationangle and a bottom portion 12B connecting inclined surfaces ofneighboring convex portions (see also FIG. 5A).

The ribbon cassette 152 is manually attached by an operator to acassette attachment portion in the apparatus body. The cassetteattachment portion is configured as a part of a printing portion 150(which will be described later). The cassette attachment portion has: acassette retaining member (not shown) that is abutted to the cassettecase 30 to retain the ribbon cassette 152 at a plurality of positions;an engaging portion for engaging the engaging portion 12 to theapparatus body; and a touch sensor (not shown) for detecting theattachment of the ribbon cassette 152.

As shown in FIG. 4, the apparatus body-side engaging portion to theengaging portion 12 of the winder spool 155 is configured by a pluralityof members. Specifically, a support axis 25 is fixed to the apparatusframe (the casing 102). The support axis 25 axially supports theengaging member 23 in a rotatable manner. The engaging member 23 has adisk-like shape and has gears at the outer edge. A side of the engagingmember 23 engaged with the engaging portion 12 has two engaging convexportions 22 provided in a protruded manner. The engaging convex portions22 have a shape different from those of the convex portions (grooveportions) of the engaging portion 12 and are provided so as to beopposed to each other (so as to create a phase difference of 180° in therotation direction of the engaging member 23). A spring 24 is woundaround the support axis 25. This spring 24 biases the engaging member 23(the engaging convex portion 22) toward the engaging portion 12 in aslidable manner (see also FIG. 5A).

As shown in FIG. 6, there may be a case where, when the ribbon cassette152 is attached to the cassette attachment portion, the tip end of theconvex portion of the engaging portion 12 of the spool body 10 isabutted to (or collides with) the tip end of the engaging convex portion22 provided in the apparatus body-side engaging member 23 and isprevented from being smoothly inserted. The engaging member 23 isslidably provided in the axial direction of the support axis 25. Thus,when the tip end of the convex portion of the engaging portion 12collides with the tip end of the engaging convex portion 22, theengaging convex portion 22 is once evacuated to the apparatus frame-side(the opposite side of the spool body 10). Thereafter, when the engagingmember 23 or the spool body 10 is rotated, the engaging convex portion22 enters the groove between the convex portions of the engaging portion12 and is biased by the spring 24 toward the spool body 10 and theengaging convex portion 22 is in a point contact with (the groove)between the convex portions the engaging portion 12 at two points (seeFIG. 5A).

As shown in FIG. 4, the gear of the engaging member 23 is meshed with agear 21C. The gear 21C is fixed with a rotation plate 21A in which aslit (not shown) is coaxially provided. At a position adjacent to therotation plate 21A, a transmission integration-type sensor 21Bconsisting of a light-emitting element and a light-receiving element isprovided. Thus, the rotation plate 21A and the sensor 21B configure anencoder 21 that detects the rotation amount of the winder spool 155around which the ink ribbon R is wound. The gear of the engaging member23 is meshed with the gear 26. The gear 26 is coaxially engaged with themotor axis of the stepping motor M (see also FIG. 2).

On the other hand, the apparatus body-side engaging portion of thesupply spool 154 to the engaging portion 12 is basically the same as theabove-described apparatus body-side engaging portion of the winder spool155 to the engaging portion 12. However, the former is different fromthe latter in that the gear 26 and a motor M are substituted with a gearmeshed with the gear of the engaging member 23 and a torque limiter (notshown) that is coaxially provided with this gear and that applies a backtension to the ink ribbon R.

The following portion will describe, with reference to FIG. 5, onefeature of the present invention by describing how the engaging convexportions 22 of the supply spool 154 and the winder spool 155 are engagedwith the engaging portion 12 of the spool body 10.

FIG. 5A illustrates how the engaging convex portion 22 is engaged withthe engaging portion 12. In FIG. 5A, it is notable that: (1) theengaging convex portion 22 has a different shape from that of the convexportion of the engaging portion 12 (the inclination angle of the sideface 22A of the engaging convex portion 22 is different from theinclination angle of the groove formed by the convex portions of theengaging portion 12); and (2) the engaging convex portion 22 is in apoint contact with (the groove formed by) the convex portions of theengaging portion 12 at two points. In the case of the conventionalprinting apparatus such as a printer apparatus, the convex portion ofthe apparatus body is engaged with the convex portion of the spool bodyhaving the same shape as that of the convex portion of the apparatusbody, which has caused a backlash due to the line contact of the engagedportions. According to this engaging form, the former and the latterhave different shapes to have a point contact at two-points to prevent abacklash. The engaging convex portion 22 is biased by the spring 24toward the engaging portion 12 to secure a stronger engaging statetherebetween, thus reducing a possibility of the generation of thebacklash.

However, as shown in FIG. 5B and FIG. 5C, the engaging form as describedabove also can be applied to other forms. Specifically, the following isestablished when an inclination angle from the horizontal plane of theconvex portion of the engaging portion 12 is represented as α, and aninclination angle from the horizontal plane of the engaging convexportion 22 is represented as β.

i) In the case of 0°<α<90°

Contact points (abutting points) a and b of the engaging portion 12 andthe engaging convex portion 22 are the inclined surface 12A of theconvex portion of the engaging portion 12 and the vertex (corner) of theengaging convex portion 22. In this case, α<β is established.

ii) In the Case of 90°≦α<180°

The contact points a and b of the engaging portion 12 and the engagingconvex portion 22 are the vertex (corner) of the convex portion of theengaging portion 12 and the side face 22A of the engaging convexportion. In this case, β<90° is established.

As shown in FIG. 2, at the downstream of the direction along which acard is carried by the carry roller 143, the printing portion 150 isprovided. The printing portion 150 prints predetermined characters orimage on the surface of a card C cleaned by the cleaning roller 131.

In this form, the printing portion 150 is composed by a thermal transferprinter. The printing portion 150 has the thermal head 151 that isprovided so as to be able to move closer to or away from a platen roller144 provided at the printing position on a card carrying path P1. Theplaten roller 144 and the thermal head 151 have therebetween the inkribbon R on which a plurality of colors such as ink layers Y (yellow), M(magenta), C (cyan), Bk (black) or the like are frame-sequentiallyrepeated.

When information such as the one for characters or image is recorded onthe card C moved along the card carrying path P1 through thermaltransfer, the ink ribbon R is supplied from the supply spool 154 and iscarried while the substantially entire surface thereof is abutted to thetip end of the thermal head 151 and is wound around the winder spool155. The supply spool 154 and the winder spool 155 are rotated by thedriving by the motor M. Then, a heating element of the thermal head 151is selectively operated while pressurizing the thermal head 151 to thecard C having thereon the ink ribbon R to print the predeterminedcharacters or image on the card C. The path along which the ink ribbon Ris carried has a transmission-type sensor. The transmission-type sensorconsists of a plurality of guide shafts, a light-emitting element 158for detecting the ink layer Bk (black) to locate a predetermined inklayer (ink layer Y in this form), and a light-receiving element 159.

The following portion will describe the locating of the ink ribbon Rcarried out just before a printing processing. The CPU provided in acontroller 195 drives a motor (not shown) to wind the ink ribbon R inthe ribbon cassette 152 around the winder spool 155. When atransmission-type sensor consisting of the light-emitting element 158and the light-receiving element 159 detects an end of the ink layer Bk(black) (when the light-receiving element 159 detects that the lightemitted from the light-emitting element 158 once blocked by the inklayer Bk is now transmitted), the CPU triggers the further driving of amotor (not shown) of a predetermined number of steps to locate the inkribbon R so that the tip end of the ink layer Y (yellow) is positionedat the positions of the thermal head 151 and the platen roller 144.

It is noted that, since the width of the ink layer Bk of the ink ribbonR (a width between the tip end and a rear end) is fixed (or known) inthis form, the CPU counts the number of pulses inputted to the motor Mto use the transmission-type sensor consisting of the light-emittingelement 158 and the light-receiving element 159 to detect the tip endand the rear end of the ink layer Bk. The CPU also can know the rotationamount of the encoder 2 of the supply spool 154 (and optionally therotation amount of the encoder of the winder spool 155) to accuratelycalculate the carrying amount of the ink ribbon R.

A subsequent printing processing is disclosed in U.S. Ser. No.12/003,260.

Next, the effect or the like of the printer apparatus 100 of thisembodiment will be described together with the effect or the like of theribbon cassette 152 (the spool body 10) attached to or detached from theprinter apparatus 100.

As described above, in this embodiment, the convex portion of theengaging convex portion 22 has a different shape from that of the convexportion of the engaging portion 12 and the convex portion of theengaging convex portion 22 has a point contact with the convex portionof the engaging portion 12 at two points (see FIG. 6). According to theprinter apparatus 100 of this embodiment, the engaging convex portion 22having a point contact with the engaging portion 12 at two points canallow the engaging portion 12 of the spool body 10 to engage theengaging convex portion 22 of the apparatus body-side engaging member 23without having a backlash, thus allowing the encoder 21 to accuratelydetect the actual rotation amount of the spool body 10. Therefore, theink ribbon R can be accurately located and can be prevented from beingmislocated, thus preventing a printing error such as a case where anunintended color is printed for example.

Furthermore, in this embodiment, the engaging convex portion 22 can bebiased by the spring 24 toward the engaging portion 12 to secure astronger engaging state between the engaging convex portion 22 and theengaging portion 12. Thus, this embodiment reduces the possibility of abacklash.

It is noted that, although this embodiment has described an example inwhich the flanges 13 and 14 are provided at both sides of the ribbonretaining portion 18 of the spool body 10, the present invention is notlimited to this example. For example, the flange 14 also may be providedto the cassette case 30 so as to regulate the position of the ink ribbonR in the axial direction of the spool body 10. Although this embodimenthas described an example in which the axis portion 19 of the spool body10 is provided to protrude form the flange 14, the present invention isnot limited to this. For example, the cassette case 30 also may have anaxis portion to support the ribbon spool body 10 in a rotatable manner.

Although this embodiment has described an example in which both of thesupply spool 154 and the winder spool 155 use the spool body 10 shown inFIG. 4, the spool body 10 shown in FIG. 4 provided at any one of thesupply spool 154 and the winder spool 155 also can contribute to animproved operability or the apparatus having a smaller size to someextent. Although this embodiment has shown an embodiment in which thegroove of the engaging portion 12 of the ribbon spool is engaged withthe engaging convex portion 22A of the engaging member 23, the sameeffect also can be obtained by another configuration where the engagingmember 23 includes a groove that is engaged with the convex portion 12of the ribbon spool.

The disclosure of Japanese Patent Application No. 2007-172511, filed onJun. 29, 2007, is incorporated in the application.

While the invention has been explained with reference to the specificembodiments of the invention, the explanation is illustrative and theinvention is limited only by the appended claims.

1. A ribbon spool for detachably attaching to a printing apparatus forforming an image on a recording medium by an ink ribbon, said printingapparatus having an engaging member including an engaging convexportion, comprising: a ribbon retaining portion for retaining the inkribbon; and an engaging portion provided at one lateral side end of theribbon spool for engaging the engaging convex portion and having aplurality of inclined grooves, wherein the grooves have an inclinationangle different from that of a lateral side face of the engaging convexportion, at least one of the grooves of the engaging portion having apoint contact with the engaging convex portion at two points to engagethe engaging convex portion.
 2. A ribbon spool according to claim 1,wherein the grooves of the engaging portion have convex portions in ashape different from a shape of the engaging convex portion.
 3. A ribbonspool according to claim 1, wherein in case the grooves of the engagingportion have an inclination angle α and the lateral side face of theengaging convex portion has an inclination angle β, when α is 0°<α<90°(wherein α<β), the two points correspond to inclined surface of theconvex portion of the engaging portion and vertex of the engaging convexportion, and wherein, when α is 90°≦α<180° (wherein β<90°), the twopoints correspond to vertexe of the convex portion of the engagingportion and lateral side face of the engaging convex portion.
 4. Aribbon spool according to claim 1, wherein the ribbon retaining portionhas a flange for regulating a position of the ink ribbon in an axialdirection, and the engaging portion is adjacent to the flange.
 5. Aribbon cassette, comprising: a supply spool for supplying an ink ribbon;a winder spool around which the ink ribbon is wound; and a case forrotatably storing the supply spool and the winder spool; wherein atleast one of the supply spool and the winder spool is the ribbon spoolaccording to claim
 1. 6. A ribbon cassette, comprising: a supply spoolfor supplying the ink ribbon; a winder spool around which the ink ribbonis wound; and a case for rotatably storing the supply spool and thewinder spool; wherein at least one of the supply spool and the winderspool is the ribbon spool according to claim
 2. 7. A ribbon cassette,comprising: a supply spool for supplying the ink ribbon; a winder spoolaround which the ink ribbon is wound; and a case for rotatably storingthe supply spool and the winder spool; wherein at least one of thesupply spool and the winder spool is the ribbon spool according to claim3.
 8. A ribbon cassette, comprising: a supply spool for supplying theink ribbon; a winder spool around which the ink ribbon is wound; and acase for rotatably storing the supply spool and the winder spool;wherein at least one of the supply spool and the winder spool is theribbon spool according to claim
 4. 9. A printing apparatus for formingan image on a recording medium by an ink ribbon situated in a ribbonspool having a ribbon retaining portion for retaining the ink ribbon,and an engaging portion provided at one lateral side end and having aplurality of inclined grooves, comprising: an engaging member forengaging the engaging portion of the ribbon spool, said engaging memberhaving an engaging convex portion for engaging at least one of thegrooves of the engaging portion, wherein the engaging convex portion forengaging the engaging portion has a lateral side face with inclinationangle different from that of the grooves of the engaging portion, andthe engaging convex portion has a point contact with the at least onegroove at two points.
 10. A printing apparatus according to claim 9,wherein the engaging convex portion has a shape different from those ofthe convex portions of the engaging portion.
 11. A printing apparatusaccording to claim 9, wherein in case the grooves of the engagingportion have an inclination angle α, and the lateral side face of theengaging convex portion has an inclination angle β, when α is 0°<α<90°(wherein α<β), the two points correspond to an inclined surface of theconvex portions of the engaging portion and vertex of the engagingconvex portion, and wherein when α is 90°≦α<180° (wherein β<90°), thetwo points correspond to vertex of the convex portions of the engagingportion and a side face of the engaging convex portion.
 12. A printingapparatus according to claim 9, wherein the engaging member has biasingmeans for biasing the ribbon spool, and the biasing means biases theengaging convex portion toward the engaging portion.
 13. A printingapparatus according to claim 9, further comprising an encoder connectedto the engaging member for detecting a rotation amount of the ribbonspool.
 14. A combination of a ribbon spool and a printing apparatus forforming an image on a recording medium by an ink ribbon, wherein saidprinting apparatus includes an engaging member having an engaging convexportion, and wherein said ribbon spool includes a ribbon retainingportion for retaining the ink ribbon; and an engaging portion providedat one lateral side end of the ribbon spool for engaging the engagingconvex portion and having a plurality of inclined grooves, wherein thegrooves have an inclination angle different from that of a lateral sideface of the engaging convex portion, at least one of the grooves of theengaging portion having a point contact with the engaging convex portionat two points to engage the engaging convex portion.
 15. A combinationaccording to claim 14, wherein the grooves of the engaging portion haveconvex portions in a shape different from a shape of the engaging convexportion.
 16. A combination according to claim 14, wherein in case thegrooves of the engaging portion have an inclination angle α and thelateral side face of the engaging convex portion has an inclinationangle β, when α is 0°<α<90° (wherein α<β), the two points correspond toinclined surface of the convex portion of the engaging portion andvertex of the engaging convex portion, and wherein when α is 90°≦α<180°(wherein β<90°), the two points correspond to vertexe of the convexportion of the engaging portion and lateral side face of the engagingconvex portion.
 17. A combination according to claim 14, wherein theribbon retaining portion has a flange for regulating a position of theink ribbon in an axial direction, and the engaging portion is adjacentto the flange.